1. Field of the Invention
The present invention relates to a volume phase type hologram, particularly to a volume phase type hologram in the form of a film, and a photosensitive resin composition employed therefor.
2. Related Background Art
Gelatin sensitized by a dichromate has hitherto been widely known and employed for recording medium for volume phase type hologram. Other kinds of recording mediums are also known for forming volume phase type hologram comprising a hydrophobic polymer, exemplified by poly(N-vinylcarbazole), (hereinafter referred to as PVCz) sensitized by addition of an iodine compound, which are disclosed in detail in prior art publications such as U.S. Pat. No. 4,172,724, U.S. Pat. No. 4,258,111 and U.S. Pat. No. 4,287,277.
The volume phase type hologram is employed for recording the interference wave of laser beams in a thin film of 20 .mu.m thick or less. In use with a visible light laser, the layer of photosensitive material for halogram recording is required to be fixed with accuracy of approximately from 0.01 to 0.02 .mu.m during exposure in order to record a Bragg's lattice of approximately 0.1 to 0.2 .mu.m interstice within a film.
In after-treatment subsequent to the exposure, the photosensitive recording layer is swelled and then shrinked to modulate the refractive index of the portion recorded by a laser beam, where the recording layer has to be swelled and then shrinked only in a direction substantially perpendicular to the recording layer. Because of such restriction both in light exposure and in after-treatment, conventional volume phase type holograms have been tightly fixed and supported on a rigid substrate plate.
With the development of holography technology, application for the hologram itself are expanding not only in the conventional optical parts such as laser-protecting goggles, head-up display devices, but also in various fields typically amusement of stereopicture itself, ornament of articles, etc. Accordingly, various kinds of volume phase type hologram are required for the application fields.
On the other hand, the aforementioned recording mediums for the volume phase type hologram are not able to satisfy the properties of hologram proposed by the expanding application.